S2091 A Retrospective Review of Antibiotic Infusion for Symptomatic Blastocystis hominis and Dientamoeba fragilis Infections

Introduction: Blastocystis hominis and Dientamoeba fragilis are intestinal parasites commonly associated with a range of symptoms. Treatment is often sought but the optimal therapeutic strategy remains unclear in part due to the inability to perform antibiotic sensitivities. We analysed the efficacy of antibiotic infusion therapy at the Centre for Digestive Diseases (CDD). Methods: Data was collected from 154 patients (aged 17-82) who underwent antibiotic infusion between January 2023 and April 2025 at CDD. Patients without post treatment results were excluded (n = 32). Pathogen, symptoms, treatment regimen, and polymerase chain reaction (PCR) outcomes were analyzed. Treatment success was a negative PCR result post infusion. Logistic regression was used to explore potential predictors of treatment success. Results: Of those included in the study 92 (59.7%) had Blastocystis only, 31 (20.1%) had Dientamoeba only, and 31 (20.1%) had both. All patients were symptomatic with the most common symptoms being bloating (n = 114, 77%), diarrhea (n = 105, 70.9%), flatulence (n = 107, 72.3%), abdominal discomfort (n = 95, 64.2%), and fatigue (n = 93, 62.8%). The overall success rate was 95.45%. The standard infusion combination (furazolidone, nitazoxanide, secnidazole) given to 47 patients (30.5%) had a success rate of 97.87%. Forty-eight patients (31.2%) received a stronger combination (incorporating first and second line treatments to provide broader coverage) (nitazoxanide, paromomycin, diloxanide furoate) which had a success rate of 97.92%. Remaining patients (n = 59, 38.3%) received alternative infusions that involved different combinations and resulted in a lower success rate of 91.53%. Reinfection which was defined as a positive PCR result following a negative result post treatment occurred in 2 patients (1.3%). No statistically significant predictors of treatment outcome were identified. Conclusion: The high success rates and low reinfection rates of the antibiotic infusion treatment show that this is a promising treatment method. This study is limited by missing clinical data, its retrospective design, the absence of documented adverse events, and the subjective manner in which symptoms were recorded. Prospective studies are required to assess symptom resolution, long-term outcomes, adverse events, and pathogenesis of these parasitic infections.